This invention relates to a system for detecting various types of pulsed signals, such as teletype, automatic Morse, manual Morse, and similar types of pulsed signals that are used in communicating. This detecting or recognition of a signal type is accomplished by determining the ratio of consecutive signal element widths and providing an output pulse having an amplitude that is a function of this ratio.
Ratio analysis is a useful and convenient method of analysis because it essentially normalizes the speed of transmission. In signal recognition once the rate has been determined, it is desirable to make the rest of the system as independent of rate as possible. Ratio analysis accomplishes this by examining the successive ratios of the signal element intervals. Mark-to-mark or space-to-space ratios can be used. The ratio distribution for machine Morse, manual Morse, teleprinter, and other possible signals in the expected environment are quite distinct and separable.
For Morse signals, almost every ratio falls into one of three discrete classes: either a 1:1, a 1:3, or a 3:1 ratio of pulse widths are present over 95 percent of the time. For teleprinter and all other signals in the environment, the frequency of occurrence of these ratios is quite low. Of course, a tolerance around these discrete ratios is necessary to account for possible bias on automatic Morse transmissions and the erratic distributions of manual Morse transmission. Besides separating all Morse signals from other transmissions, the ratio analyzer herein set forth will provide an output signal for distinguishing automatic Morse from manual Morse by the indication of the actual tightness of the ratio distribution.